From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:42998 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728767AbeLMMP6 (ORCPT ); Thu, 13 Dec 2018 07:15:58 -0500 Date: Thu, 13 Dec 2018 12:15:49 +0000 From: "Dr. David Alan Gilbert" To: David Hildenbrand Cc: Vivek Goyal , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, miklos@szeredi.hu, stefanha@redhat.com, sweil@redhat.com, swhiteho@redhat.com Subject: Re: [PATCH 18/52] virtio-fs: Map cache using the values from the capabilities Message-ID: <20181213121548.GN2313@work-vm> References: <20181210171318.16998-1-vgoyal@redhat.com> <20181210171318.16998-19-vgoyal@redhat.com> <20181213091320.GA2313@work-vm> <20181213100058.GC2313@work-vm> <96d9ea85-ddf3-3331-77ce-124475b26da4@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <96d9ea85-ddf3-3331-77ce-124475b26da4@redhat.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: * David Hildenbrand (david@redhat.com) wrote: > On 13.12.18 11:00, Dr. David Alan Gilbert wrote: > > * David Hildenbrand (david@redhat.com) wrote: > >> On 13.12.18 10:13, Dr. David Alan Gilbert wrote: > >>> * David Hildenbrand (david@redhat.com) wrote: > >>>> On 10.12.18 18:12, Vivek Goyal wrote: > >>>>> Instead of assuming we had the fixed bar for the cache, use the > >>>>> value from the capabilities. > >>>>> > >>>>> Signed-off-by: Dr. David Alan Gilbert > >>>>> --- > >>>>> fs/fuse/virtio_fs.c | 32 +++++++++++++++++--------------- > >>>>> 1 file changed, 17 insertions(+), 15 deletions(-) > >>>>> > >>>>> diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c > >>>>> index 60d496c16841..55bac1465536 100644 > >>>>> --- a/fs/fuse/virtio_fs.c > >>>>> +++ b/fs/fuse/virtio_fs.c > >>>>> @@ -14,11 +14,6 @@ > >>>>> #include > >>>>> #include "fuse_i.h" > >>>>> > >>>>> -enum { > >>>>> - /* PCI BAR number of the virtio-fs DAX window */ > >>>>> - VIRTIO_FS_WINDOW_BAR = 2, > >>>>> -}; > >>>>> - > >>>>> /* List of virtio-fs device instances and a lock for the list */ > >>>>> static DEFINE_MUTEX(virtio_fs_mutex); > >>>>> static LIST_HEAD(virtio_fs_instances); > >>>>> @@ -518,7 +513,7 @@ static int virtio_fs_setup_dax(struct virtio_device *vdev, struct virtio_fs *fs) > >>>>> struct dev_pagemap *pgmap; > >>>>> struct pci_dev *pci_dev; > >>>>> phys_addr_t phys_addr; > >>>>> - size_t len; > >>>>> + size_t bar_len; > >>>>> int ret; > >>>>> u8 have_cache, cache_bar; > >>>>> u64 cache_offset, cache_len; > >>>>> @@ -551,17 +546,13 @@ static int virtio_fs_setup_dax(struct virtio_device *vdev, struct virtio_fs *fs) > >>>>> } > >>>>> > >>>>> /* TODO handle case where device doesn't expose BAR? */ > >>>> > >>>> For virtio-pmem we decided to not go via BARs as this would effectively > >>>> make it only usable for virtio-pci implementers. Instead, we are going > >>>> to export the applicable physical device region directly (e.g. > >>>> phys_start, phys_size in virtio config), so it is decoupled from PCI > >>>> details. Doing the same for virtio-fs would allow e.g. also virtio-ccw > >>>> to make eventually use of this. > >>> > >>> That makes it a very odd looking PCI device; I can see that with > >>> virtio-pmem it makes some sense, given that it's job is to expose > >>> arbitrary chunks of memory. > >>> > >>> Dave > >> > >> Well, the fact that your are > >> > >> - including > >> - adding pci related code > >> > >> in/to fs/fuse/virtio_fs.c > >> > >> tells me that these properties might be better communicated on the > >> virtio layer, not on the PCI layer. > >> > >> Or do you really want to glue virtio-fs to virtio-pci for all eternity? > > > > No, these need cleaning up; and the split within the bar > > is probably going to change to be communicated via virtio layer > > rather than pci capabilities. However, I don't want to make our PCI > > device look odd, just to make portability to non-PCI devices - so it's > > right to make the split appropriately, but still to use PCI bars > > for what they were designed for. > > > > Dave > > Let's discuss after the cleanup. In general I am not convinced this is > the right thing to do. Using virtio-pci for anything else than pure > transport smells like bad design to me (well, I am no virtio expert > after all ;) ). No matter what PCI bars were designed for. If we can't > get the same running with e.g. virtio-ccw or virtio-whatever, it is > broken by design (or an addon that is tightly glued to virtio-pci, if > that is the general idea). I'm sure we can find alternatives for virtio-*, so I wouldn't expect it to be glued to virtio-pci. Dave > -- > > Thanks, > > David / dhildenb -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK